Semiconductor device pre-cleaning

ABSTRACT

An ammonium fluoride gas may be used to form a protection layer for one or more interlayer dielectric layers, one or more insulating caps, and/or one or more source/drain regions of a semiconductor device during a pre-clean etch process. The protection layer can be formed through an oversupply of nitrogen trifluoride during the pre-clean etch process. The oversupply of nitrogen trifluoride causes an increased formation of ammonium fluoride, which coats the interlayer dielectric layer(s), the insulating cap(s), and/or the source/drain region(s) with a thick protection layer. The protection layer protects the interlayer dielectric layer(s), the insulating cap(s), and/or the source/drain region(s) during the pre-clean process from being etched by fluorine ions formed during the pre-clean process.

BACKGROUND

As processing nodes for transistors shrink, and as transistor densityincreases, the available spacing between the gate of a transistor andthe source contact and drain contact decreases and/or is eliminatedentirely. A self-aligned contact (SAC) process is a process by which acontact for a source/drain region of a transistor is at least partiallyformed over a metal gate (MG) of the transistor. An insulating cap isformed over the MG to electrically isolate the MG from the contact (thecontact may be referred to as a metal drain or a metal on operationdomain (MD)). In this way, the SAC process may be used to permit furtherreductions in processing node sizes, to permit increased transistordensities for semiconductor devices, and/or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a diagram of an example environment in which systems and/ormethods described herein may be implemented.

FIGS. 2A-2J are diagrams of one or more example implementationsdescribed herein.

FIG. 3 is an illustration of an example semiconductor structure formedbased on the example techniques described in connection with FIGS.2A-2J.

FIG. 4 is a diagram of an example of epitaxial window data associatedwith one or more semiconductor structures described herein.

FIG. 5 is a diagram of example components of one or more devices of FIG.1.

FIGS. 6-8 are flowcharts of example processes for semiconductor devicepre-cleaning.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

In a self-aligned contact (SAC) process, an SAC contact may be formed toconnect a source region or a drain region of a semiconductor device(e.g., a transistor, a memory device, and/or the like) to a conductivelayer. To decrease resistance between the source/drain region and theconductive layer, a metal silicide (e.g., titanium silicide (TiSi) oranother type of metal silicide) may be applied to the top surface of thesource/drain region prior to formation of the contact. The top surfaceof the source/drain region may be prepared for the metal silicide usinga pre-clean process (e.g., an epitaxial pre-clean process, a silicidepre-clean process, and/or the like) to remove residual oxides and othercontaminates. After the pre-clean, a metal layer (e.g., a titaniumlayer) is formed over the source/drain region, and the wafer issubjected to a high-temperature anneal which causes the metal to reactwith silicon to form the metal silicide layer.

However, the pre-clean process (as well as various etch processes duringformation of the self-aligned contacts) may cause excessive removal ofprotective interlayer dielectric (ILD) material from the transistor anda silicon nitride (e.g., Si_(x)N_(y), such as Si₃N₄) material from theinsulating cap that isolates a metal drain (MD) of the semiconductordevice from the SAC contact. This can increase the risk of shortingbetween the MD and a metal gate (MG) of the semiconductor device, canincrease SAC loss loading for the semiconductor device, can decrease anepitaxial loss window for the semiconductor device, and/or the like.

Some implementations described herein provide techniques and apparatusesfor using an ammonium fluoride (NH₄F) gas to form a protection layer forone or more interlayer dielectric layers, one or more insulating caps,and/or one or more source/drain regions of a semiconductor device duringa pre-clean etch process. The protection layer can be formed through anoversupply of nitrogen trifluoride (NF₃) during the pre-clean etchprocess. The oversupply of nitrogen trifluoride may be provided byincreasing the flow-in of nitrogen trifluoride relative to a traditionalamount of nitrogen trifluoride used during a pre-clean process. Theoversupply of nitrogen trifluoride causes an increased formation of anammonium fluoride gas, which deposits onto the interlayer dielectriclayer(s), the insulating cap(s), and the source/drain region(s) as athick protection layer. The ammonium fluoride in the protection layercleans an oxide layer from the interlayer dielectric layer(s), theinsulating cap(s), and the source/drain region(s) during the pre-cleanprocess by reacting with the oxide layer to form ammoniumfluorosilicate. The ammonium fluorosilicate may be decomposed into oneor more gasses through heating at the end of or after the pre-cleanprocess, which are then removed from a pre-clean chamber.

In this way, the protection layer protects the interlayer dielectriclayer(s), the insulating cap(s), and the source/drain region(s) duringthe pre-clean process from being etched by fluorine ions formed duringthe pre-clean process. This may reduce the risk of an MG/MD short, mayreduce SAC loss loading for the semiconductor device (e.g., may reducethe amount of insulating layer loss during the pre-clean process), mayincrease the epitaxial loss window for the semiconductor device (e.g.,may increase the temperature window for the pre-clean process, which mayprotect against temperature drift), and/or the like.

FIG. 1 is a diagram of an example environment 100 in which systemsand/or methods described herein may be implemented. As shown in FIG. 1,environment 100 may include a pre-clean tool 102, a deposition tool 104,an annealing tool 106, a plating tool 108, and a wafer/die transportdevice 110. The tools and/or devices included in example environment 100may be included in a semiconductor clean room, a semiconductor foundry,a semiconductor processing and/or manufacturing facility, and/or thelike.

Pre-clean tool 102 includes a pre-clean chamber 112 and one or moredevices capable of performing a pre-clean process on a semiconductordevice to remove an oxide layer from the semiconductor device. The oneor more devices may include a gas source 114, a plasma source 116, aheat source 118, and/or the like. The gas source 114 may supply variousgasses to pre-clean chamber 112, such as an ammonia gas, a nitrogentrifluoride gas, and/or the like. Plasma source 116 may generate aplasma that causes a reaction between the gasses supplied to pre-cleanchamber 112. For example, plasma source 116 includes an inductivelycoupled plasma (ICP) source, a transformer coupled plasma (TCP) source,or another type of plasma source capable of causing a reaction betweenan ammonia gas and a nitrogen trifluoride gas to cause the formation ofan ammonium fluoride gas. Heat source 118 may be capable of heating asemiconductor device in pre-clean chamber 112 to cause one or morelayers on the semiconductor device to decompose, as described herein.For example, heat source 118 may include a heat lamp, a heating coil, oranother type of heating device that heats the semiconductor device tocause a protection layer on the semiconductor device to decompose intoone or more gasses, as described herein.

Deposition tool 104 is a semiconductor processing tool that includes asemiconductor processing chamber and one or more devices capable ofdepositing various types of materials onto a semiconductor device. Forexample, deposition tool 104 may include a chemical vapor depositiondevice (e.g., an electrostatic spray device, an epitaxy device, and/oranother type of chemical vapor deposition device), a physical vapordeposition device (e.g., a sputtering device and/or another type ofphysical vapor deposition device), and/or the like. In someimplementations, deposition tool 104 may deposit a metal layer onto asource region or a drain region of a semiconductor device, may deposit acontact material to form a contact (e.g., an SAC contact) of asemiconductor device, and/or the like as described herein.

Annealing tool 106 is a semiconductor processing tool that includes asemiconductor processing chamber and one or more devices capable ofheating a semiconductor device. For example, annealing tool 106 mayinclude a rapid thermal anneal (RTA) tool or another type of annealingtool that is capable of heating a semiconductor device to cause areaction between two or more materials or gasses, to cause a material todecompose, and/or the like. For example, annealing tool 106 may heat asemiconductor device to cause a metal layer on an epitaxial region(e.g., a source region or a drain region) to react and form a metalsilicide layer, as described herein.

Plating tool 108 is a semiconductor processing tool that includes asemiconductor processing chamber and one or more devices capable ofplating a semiconductor device with one or more metals. Plating, andparticularly electroplating, is a process by which metal structures areformed on a substrate (e.g., a semiconductor wafer, a semiconductordevice, and/or the like). Plating may include applying a voltage acrossan anode formed of a plating material and a cathode (e.g., a substrate).The voltage causes a current to oxidize the anode, which causes therelease of plating material ions from the anode. These plating materialions form a plating solution that travels through a plating bath towardthe substrate. The plating solution reaches the substrate and depositsplating material ions into trenches, vias, interconnects, contacts,metal layers, and/or other structures in and/or on the substrate.

In some implementations, plating tool 108 may include a copperelectroplating tool, an aluminum electroplating tool, a nickelelectroplating tool, a titanium electroplating tool, a tinelectroplating tool, a compound material or alloy (e.g., tin-silver,tin-lead, and/or the like) electroplating tool, and/or an electroplatingtool for one or more other types of conductive materials, metals, and/orthe like. In some implementations, plating tool 108 may form a metallayer on a source region or a drain region of a semiconductor device,may form a contact (e.g., an SAC contact) of a semiconductor device,and/or the like as described herein.

Wafer/die transport device 110 includes a mobile robot, a robot arm, atram or rail car, and/or another type of device that are used totransport wafers and/or dies between semiconductor processing devices102-108 and/or to and from other locations, such as a wafer rack, astorage room, and/or the like. In some implementations, wafer/dietransport device 110 may be a programmed device to travel a particularpath and/or may operate semi-autonomously or autonomously.

The number and arrangement of devices and networks shown in FIG. 1 areprovided as one or more examples. In practice, there may be additionaldevices, fewer devices, different devices, or differently arrangeddevices than those shown in FIG. 1. Furthermore, two or more devicesshown in FIG. 1 may be implemented within a single device, or a singledevice shown in FIG. 1 may be implemented as multiple, distributeddevices. Additionally, or alternatively, a set of devices (e.g., one ormore devices) of environment 100 may perform one or more functionsdescribed as being performed by another set of devices of environment100.

FIGS. 2A-2J are diagrams of one or more example implementations 200described herein. Example implementation(s) 200 may include one or moreexample implementations of forming one or more parts of a semiconductordevice using an ammonium fluoride protection layer. The semiconductordevice may include a transistor (e.g., a metal oxide field effecttransistor (MOSFET) or another type of transistor), a memory device(e.g., a static random access memory (SRAM) or another type of memorydevice), and/or the like.

As shown in FIG. 2A, the semiconductor device may include variousstructures formed in and/or on a substrate (e.g., a semiconductorwafer), such as an active region, one or more source regions and/ordrain regions, one or more metal gates (MGs), one or more gate spacers,one or more insulating caps, one or more interlayer dielectric (ILD)layers, and/or the like. The active region (which, in some cases, may bereferred to as an operation domain) may include a material thatelectrically insulates the metal gate(s) and the source/drain region(s)of the semiconductor device from other portions of the semiconductordevice. For example, the active region may include tantalum nitride(TaN), a silicon oxide (e.g., SiO_(x), such as SiO or SiO₂), silicateglass, silicon oxycarbide, and/or the like. The interlayer dielectriclayer(s) may include an electrically insulating material thatelectrically insulates the structures from other portions of thesemiconductor device. For example, the interlayer dielectric layer(s)may include tantalum nitride (TaN), silicon oxide (SiO_(x)), silicateglass, silicon oxycarbide, a silicon nitride (Si_(x)N_(y)), and/or thelike. In some implementations, the interlayer dielectric layer(s) may beformed to a height of around 80 nanometers or greater. The source/drainregion(s) may include a silicon germanium formed via epitaxial growthand, thus, may be referred to as epitaxial regions. In someimplementations, the source/drain region(s) each form a source/drainplug that is electrically coupled to one or more other components of thesemiconductor device.

The metal gate(s) may include an electrically conductive metal, such astitanium, cobalt, tungsten, aluminum, copper, ruthenium, iridium, and/orthe like. The metal gate(s) may be electrically isolated from trenchesin which conductors or MDs are to be formed from one or more gatespacers. The gate spacers may include electrically insulating sidewallsformed of an electrically insulating material, such as tantalum nitride(TaN), silicon oxide (SiO_(x)), silicate glass, silicon oxycarbide,silicon nitride (Si_(x)N_(y)), and/or the like.

In some implementations, the semiconductor device may be processed toform one or more SAC contacts (or SAC MD structures) over one or more ofthe source/drain regions and in trenches between the metal gates. Forexample, the semiconductor device may be processed using one or more ofthe semiconductor processing devices described above in FIG. 1. In theseexamples, a portion of the metal gates may be etched (e.g., using a dryetching process, a wet etching process, and/or the like) such that aninsulating cap may be formed over each of the metal gate(s) toelectrically insulate the top and/or portions of the side of the metalgates from the SAC conductors. The insulating cap(s) may be formed of anelectrically insulating material, such as tantalum nitride (TaN),silicon oxide (SiO_(x)), silicate glass, silicon oxycarbide, siliconnitride (Si_(x)N_(y)), and/or the like. In some implementations, theinsulating caps may be formed to an example height of around 30-60nanometers.

Prior to forming the one or more SAC contacts, a metal silicide layermay be formed in and/or on the source/drain regions to decrease contactresistance between the SAC contacts and the source/drain regions, and todecrease contact resistance between the SAC conductors and a conductivelayer that is to be formed above the SAC contacts. An oxide layer may beremoved from various portions of the semiconductor device to prepare thesource/drain regions for metal silicide formation. The oxide layer mayinclude residual material, such as a silicon oxide, that formed on thevarious portions of the semiconductor as a result other semiconductorprocesses. This oxide layer may otherwise cause increased contactresistance if not removed.

As shown in FIG. 2B, the semiconductor device may be placed in apre-clean chamber so that a pre-clean process can be performed to etch,clean, or otherwise remove the oxide layer from the semiconductordevice. The pre-clean chamber may be part of a pre-clean tool (e.g.,pre-clean chamber 112 of pre-clean tool 102), such as a Collinspre-clean tool, a silicon cobalt nickel (SiCoNi) pre-clean chamber, oranother type of pre-clean chamber. In some implementations, thepre-clean chamber may be part of another semiconductor processing toolsuch that the semiconductor device can remain in the pre-clean chamberfor the next semiconductor processing step, which prevents additionaloxide formation that otherwise might occur during transport of thesemiconductor from the pre-clean chamber to another chamber.

As further shown in FIG. 2B, and by reference number 202, a flow-in ofammonia (NH₃) gas may be provided into the pre-clean chamber (e.g., froma gas source 114). Once the flow-in is complete, the pressure may bestabilized in the pre-clean chamber.

As shown in FIG. 2C, and by reference number 204, a flow-in of anitrogen fluoride gas (e.g., nitrogen trifluoride (NF₃) gas) may beprovided into the pre-clean chamber (e.g., from a gas source 114). Theamount of ammonia gas and the amount of nitrogen fluoride gas providedinto the pre-clean chamber are such that the ammonia gas/nitrogenfluoride gas mixture in the pre-clean chamber satisfies a particularratio range or particular ratio threshold. For example, the amount ofammonia gas may be increased relative to a traditional amount of ammoniagas used for the pre-clean process such that the ammonia gas/nitrogenfluoride gas mixture in the pre-clean chamber includes more than 20%nitrogen fluoride gas (e.g., such that the ratio between nitrogenfluoride gas and the ammonia gas in the pre-clean chamber is greaterthan 1:5) to promote a sufficient or excess rate of ammonium fluoride(NH₄F) gas formation for protection of the interlayer dielectriclayer(s), the insulating cap(s), and/or the source/drain region(s)against fluorine etching.

As another example, the amount of ammonia gas and the amount of nitrogenfluoride gas may be provided into the pre-clean chamber such that afluorine gas is formed in the pre-clean chamber at a sufficient rate toetch the oxide layer while the ammonium fluoride gas is formed in thepre-clean chamber at a sufficient rate to form a protection layer toprotect the interlayer dielectric layer(s), the insulating cap(s),and/or the source/drain region(s) from being etched by the fluorine gas.In other words, the amount of ammonia gas and the amount of nitrogenfluoride gas provided into the pre-clean chamber are such that etchingor loss of the interlayer dielectric layer(s), the insulating cap(s),and/or the source/drain region(s), due to the fluorine gas and plasmaenergy in the pre-clean chamber, is reduced or prevented.

As shown in FIG. 2D, and by reference number 206, a plasma source (e.g.,plasma source 116) may be used to cause a reaction between the ammoniagas and the nitrogen fluoride gas in the pre-clean chamber. The plasmasource may include an ICP source, a TCP source, or another type ofplasma source capable of generating a plasma. The plasma source mayignite the plasma, which may cause the reaction between the ammonia gasand the nitrogen fluoride gas in the pre-clean chamber. In someimplementations, the plasma source may ignite the plasma such that theplasma source causes the reaction between the ammonia gas and thenitrogen fluoride gas during flow-in of the nitrogen fluoride gas intothe pre-clean chamber.

As further shown in FIG. 2D, the reaction between the ammonia gas andthe nitrogen fluoride gas causes the formation of an ammonium fluoridegas and a fluorine ion gas in the plasma in the pre-clean chamber. Insome implementations, the reaction between the ammonia gas and thenitrogen fluoride gas causes formation of a hydrogen fluoride (HF) gasin the pre-clean chamber. For example, the reaction between the ammoniagas and the nitrogen fluoride gas may be represented as:

NF₃+NH₃→∝NH₄F+βHF

where ∝ is greater than β.

As shown in FIG. 2E, and by reference number 208, the ammonium fluoridegas may solidify and form a protection layer during the etch process.The protection layer may be formed at or near the beginning of thepre-clean process, and may be composed of all or primarily ammoniumfluoride on and/or over the interlayer dielectric layer(s), theinsulating cap(s), and/or the source/drain region(s). The protectionlayer may solidify into a salt or another form of solid that isdeposited onto exposed portions (e.g., top surfaces, side walls,portions thereof, entire surfaces thereof, and/or the like) of theinterlayer dielectric layer(s), the insulating cap(s), and/or thesource/drain region(s).

The ammonium fluoride gas may be deposited until the protection layer issufficiently thick to cover (or substantially cover) the portions of theinterlayer dielectric layer(s), the insulating cap(s), and/or thesource/drain region(s). The thickness of the protection layer may beuniform or variable. In some implementations, the protection layer isformed on the interlayer dielectric layer(s) and the insulating cap(s)to greater than approximately 14 nm thickness. In some implementations,the protection layer is formed to approximately a 4-5 nm thickness onthe source/drain region(s).

The protection layer protects the interlayer dielectric layer(s), theinsulating cap(s), and/or the source/drain region(s) from being etchedby fluorine ions during the pre-clean process. For example, theprotection layer reduces or prevents fluorine ions or hydrogen fluoridegas from reaching the interlayer dielectric layer(s), the insulatingcap(s), and/or the source/drain region(s) and removing material from theinsulating cap(s), the interlayer dielectric layer(s), and/or thesource/drain region(s). As another example, the protection layer reducesor eliminates the plasma energy transferred to the insulating cap(s),the interlayer dielectric layer(s), and/or the source/drain region(s)from the plasma supplied to the pre-clean chamber. This reduces theamount of and/or prevents material loss from the interlayer dielectriclayer(s), the insulating cap(s), and/or the source/drain region(s)during the pre-clean process.

As further shown in FIG. 2E, and by reference number 210, the pre-cleanprocess includes cleaning the insulating cap(s), the interlayerdielectric layer(s), and/or the source/drain region(s). In particular,the ammonium fluoride in the protection layer may react with the oxidelayer on the insulating cap(s), the interlayer dielectric layer(s),and/or the source/drain region(s) to clean, etch, or otherwise removethe oxide layer from the insulating cap(s), the interlayer dielectriclayer(s), and/or the source/drain region(s). In this way, the protectionlayer protects the insulating cap(s), the interlayer dielectriclayer(s), and/or the source/drain region(s) while cleaning the oxidelayer from the insulating cap(s), the interlayer dielectric layer(s),and/or the source/drain region(s).

The use of isotropic plasma during the pre-clean process may be skipped.In this way, the increase of the amount of nitrogen fluoride in thenitrogen fluoride/ammonia gas mixture in the pre-clean chamber togreater than 20% promotes a large production of ammonium fluoride gas toincrease the effectiveness of the pre-clean process without the need forisotropic plasma. The absence or lack of isotropic plasma reduces orprevents enlargement of the gate spacers of the semiconductor device.

The chemical reaction between the ammonium fluoride in the protectionlayer and the oxide layer may result in the formation of a fluorosiliciclayer. The fluorosilicic layer may be composed of a fluorosilicic acidsalt such as ammonium fluorosilicate ((NH₄)₂[SiF₆]) in the protectionlayer. Accordingly, the protection layer may transition to beingcomposed of ammonium fluorosilicate or a combination of ammoniumfluorosilicate and ammonium fluoride as the ammonium fluoride in theprotection cleans the oxide layer from the insulating cap(s), theinterlayer dielectric layer(s), and/or the source/drain region(s). Thechemical reaction between the ammonium fluoride in the protection layerand the oxide layer is represented as:

NH₄F+SiO₂(NH₄)₂[SiF₆]+H₂O

As shown in FIG. 2F, and by reference number 212, the internaltemperature of the pre-clean chamber may be elevated such that thesemiconductor device is heated (e.g., using a heat source 118). Thesemiconductor device may be heated after completion of the pre-cleanprocess or as part of the pre-clean process. The semiconductor devicemay be heated to decompose the protection layer, which removes theprotection layer from the semiconductor device (e.g., from theinterlayer dielectric layer(s), the insulating cap(s), and/or thesource/drain region(s)). The protection layer may be decomposed byheating the semiconductor device to a temperature at or above aparticular temperature at which ammonium fluoride and/or ammoniumfluorosilicate decompose (e.g., 90 degrees Celsius or above), whichcauses the ammonium fluoride and the ammonium fluorosilicate totransition from a solid or salt to a gas. In particular, heating theprotection layer to the point of decomposition of the ammonium fluoridein the protection layer may cause a reaction that is represented as:

NH₄F→NH₃+HF

where the solid ammonium fluoride decomposes into an ammonia (NH₃) gasand a hydrogen fluoride (HF) gas. Heating the protection layer to thepoint of decomposition of the ammonium fluorosilicate in the protectionlayer may cause a reaction that is represented as:

(NH₄)₂[SiF₆]→SiF₄+HF+NH₃

where the solid ammonium fluorosilicate decomposes into one or moregasses, including silicon tetrafluoride (SiF₄) gas, hydrogen fluoride(HF) gas, and ammonia (NH₃) gas.

As shown in FIG. 2G, and by reference number 214, the various gassesfrom the decomposition of the protection layer (e.g., the ammonia gas,the hydrogen fluoride gas, and/or the silicon tetrafluoride gas) may beremoved from the pre-clean chamber. The gasses may be removed from thepre-clean chamber using a vacuum or another technique.

As shown in FIG. 2H, the semiconductor device may be placed in asemiconductor processing chamber (e.g., by a wafer/die transport device110) such as a deposition chamber, a plating chamber, or another type ofsemiconductor processing chamber such that metal silicide layer(s) maybe formed in and/or over the source/drain region(s). The semiconductorprocessing chamber may be the same chamber as the pre-clean chamber ormay be a different chamber. As shown by reference number 216, a metallayer may be formed over the source/drain region(s). The metal layer maybe formed over the source/drain region(s) by a deposition process (e.g.,a chemical vapor deposition process, a physical vapor depositionprocess, and/or the like), a plating process (e.g., an electroplatingprocess and/or the like), or another type of semiconductor process bywhich a metal layer can be formed over the source/drain region(s). Themetal layer may include a metallic material, such as titanium (Ti),nickel (Ni), or another type of metal.

As shown in FIG. 2I, and by reference number 218, an anneal (e.g., arapid thermal anneal (RTA) or another type of annealing process) may beperformed such that the semiconductor is heated (e.g., using anannealing tool 106). The elevated temperature causes the metal layer toreact with the source/drain region(s). The reaction causes the metallayer and silicon in the source/drain region(s) to form a metal silicidelayer in and/or on the source/drain region(s). The metal silicide layermay include a metal silicide, such as a titanium silicide (TiSi_(x)), anickel silicide (Ni_(x)Si), or another metal silicide, that is to reducecontact resistance between the source/drain region(s) and SAC contact(s)that are to be formed over the source/drain region(s).

As shown in FIG. 2J, and by reference number 220, SAC contact(s) may beformed on and/or over the metal layer and over the source/drainregion(s) (e.g., using a plating tool 108). The SAC contact(s) mayelectrically connect the source/drain region(s) to a metal layer of thesemiconductor device that is to be formed over SAC contact(s). The SACcontact(s) may be formed of a conductive material, such as copper (Cu),gold (Au), silver (Ag), tungsten (W), and/or the like. As further shownin FIG. 2J, the SAC contact(s) may be formed at least partially over theinsulating cap(s). The insulating cap(s) electrically isolate the SACcontact(s) and the metal gate(s) while permitting the SAC contact(s) tobe positioned closer to the metal gate(s), which increases the densityof the semiconductor device.

The number and arrangement of structures, layers, and/or the like shownin FIGS. 2A-2J are provided as an example. In practice, a semiconductordevice including additional structures and/or layers, fewer structuresand/or layers, different structures and/or layers, or differentlyarranged structures and/or layers than those shown in FIGS. 2A-2J may beprocessed according to the techniques described above in connection withFIGS. 2A-2J.

FIG. 3 is an illustration of an example portion of a semiconductordevice 300 formed based on the example techniques described inconnection with FIGS. 2A-2J. As shown in FIG. 3, semiconductor device300 may include an insulating cap formed on a metal gate (MG), one ormore source regions and/or drain regions (source/drain regions), a metalsilicide layer formed on the source/drain regions, a plurality of SACcontacts formed above the source/drain regions and on the insulatingcaps, and a plurality of gate spacers. The insulating cap and the gatespacers electrically insulate the metal gate from the SAC contacts. Asfurther shown in FIG. 3, the use of a protection layer during apre-cleaning process prior to forming the metal silicide layers resultsin reduced and/or minimal loss loading (e.g., reduced and/or minimalloss of material) for the insulating cap and the source/drain regions.

As indicated above, FIG. 3 is provided as an example. Other examples maydiffer from what is described with regard to FIG. 3.

FIG. 4 is a diagram 400 of an example of epitaxial window dataassociated with one or more semiconductor structures described herein.As shown in FIG. 4, the amount of polysilicon material loss (illustratedin diagram 400 in angstroms (Å) from an epitaxial source region or drainregion (source/drain region) may increase as the temperature(illustrated in diagram 400 in degrees Celsius) in a pre-clean chamberincreases. Without the use of a protection layer during a pre-cleanprocess, as described above in connection with FIGS. 2A-2J, theepitaxial window for a source/drain region extends to about 31 degreesCelsius, at which point, the amount of polysilicon loss for thesource/drain region significantly increases. However, the use of aprotection layer during a pre-clean process, as described above inconnection with FIGS. 2A-2J, extends or increases the epitaxial windowfor a source/drain region up to about 35 degrees Celsius. Accordingly,the use of a protection layer during a pre-clean process increases theepitaxial window for a source/drain region, which allows for temperaturefluctuations in the pre-clean chamber and relaxes temperature controlrequirements.

As indicated above, FIG. 4 is provided as an example. Other examples maydiffer from what is described with regard to FIG. 4.

FIG. 5 is a diagram of example components of a device 500. In someimplementations, pre-clean tool 102, deposition tool 104, annealing tool106, plating tool 108, and/or wafer/die transport device 110 may includeone or more devices 500 and/or one or more components of device 500. Asshown in FIG. 5, device 500 may include a bus 510, a processor 520, amemory 530, a storage component 540, an input component 550, an outputcomponent 560, and a communication interface 570.

Bus 510 includes a component that permits communication among multiplecomponents of device 500. Processor 520 is implemented in hardware,firmware, and/or a combination of hardware and software. Processor 520is a central processing unit (CPU), a graphics processing unit (GPU), anaccelerated processing unit (APU), a microprocessor, a microcontroller,a digital signal processor (DSP), a field-programmable gate array(FPGA), an application-specific integrated circuit (ASIC), or anothertype of processing component. In some implementations, processor 520includes one or more processors capable of being programmed to perform afunction. Memory 530 includes a random access memory (RANI), a read onlymemory (ROM), and/or another type of dynamic or static storage device(e.g., a flash memory, a magnetic memory, and/or an optical memory) thatstores information and/or instructions for use by processor 520.

Storage component 540 stores information and/or software related to theoperation and use of device 500. For example, storage component 540 mayinclude a hard disk (e.g., a magnetic disk, an optical disk, and/or amagneto-optic disk), a solid state drive (SSD), a compact disc (CD), adigital versatile disc (DVD), a floppy disk, a cartridge, a magnetictape, and/or another type of non-transitory computer-readable medium,along with a corresponding drive.

Input component 550 includes a component that permits device 500 toreceive information, such as via user input (e.g., a touch screendisplay, a keyboard, a keypad, a mouse, a button, a switch, and/or amicrophone). Additionally, or alternatively, input component 550 mayinclude a component for determining location (e.g., a global positioningsystem (GPS) component) and/or a sensor (e.g., an accelerometer, agyroscope, an actuator, another type of positional or environmentalsensor, and/or the like). Output component 560 includes a component thatprovides output information from device 500 (via, e.g., a display, aspeaker, a haptic feedback component, an audio or visual indicator,and/or the like).

Communication interface 570 includes a transceiver-like component (e.g.,a transceiver, a separate receiver, a separate transmitter, and/or thelike) that enables device 500 to communicate with other devices, such asvia a wired connection, a wireless connection, or a combination of wiredand wireless connections. Communication interface 570 may permit device500 to receive information from another device and/or provideinformation to another device. For example, communication interface 570may include an Ethernet interface, an optical interface, a coaxialinterface, an infrared interface, a radio frequency (RF) interface, auniversal serial bus (USB) interface, a Wi-Fi interface, a cellularnetwork interface, and/or the like.

Device 500 may perform one or more processes described herein. Device500 may perform these processes based on processor 520 executingsoftware instructions stored by a non-transitory computer-readablemedium, such as memory 530 and/or storage component 540. As used herein,the term “computer-readable medium” refers to a non-transitory memorydevice. A memory device includes memory space within a single physicalstorage device or memory space spread across multiple physical storagedevices.

Software instructions may be read into memory 530 and/or storagecomponent 540 from another computer-readable medium or from anotherdevice via communication interface 570. When executed, softwareinstructions stored in memory 530 and/or storage component 540 may causeprocessor 520 to perform one or more processes described herein.Additionally, or alternatively, hardware circuitry may be used in placeof or in combination with software instructions to perform one or moreprocesses described herein. Thus, implementations described herein arenot limited to any specific combination of hardware circuitry andsoftware.

The number and arrangement of components shown in FIG. 5 are provided asan example. In practice, device 500 may include additional components,fewer components, different components, or differently arrangedcomponents than those shown in FIG. 5. Additionally, or alternatively, aset of components (e.g., one or more components) of device 500 mayperform one or more functions described as being performed by anotherset of components of device 500.

FIG. 6 is a flowchart of an example process 600 associated withsemiconductor device pre-cleaning. In some implementations, one or moreprocess blocks of FIG. 6 may be performed by a semiconductor processingdevice (e.g., pre-clean tool 102, deposition tool 104, annealing tool106, plating tool 108, and/or the like). Additionally, or alternatively,one or more process blocks of FIG. 6 may be performed by one or morecomponents of a device 500, such as processor 520, memory 530, storagecomponent 540, input component 550, output component 560, communicationinterface 570, and/or the like.

As shown in FIG. 6, process 600 may include forming an ammonium fluoridegas in a processing chamber to cause a chemical reaction between theammonium fluoride gas and an oxide layer on a source or drain region ofa semiconductor device in the processing chamber, where the chemicalreaction causes a fluorosilicic layer to form on the source or drainregion (block 610). For example, the semiconductor processing device mayform an ammonium fluoride gas in a processing chamber to cause achemical reaction between the ammonium fluoride gas and an oxide layeron a source or drain region of a semiconductor device in the processingchamber, as described above. In some implementations, the chemicalreaction causes a fluorosilicic layer to form on the source or drainregion.

As further shown in FIG. 6, process 600 may include removing thefluorosilicic layer from the source or drain region (block 620). Forexample, the semiconductor processing device may remove thefluorosilicic layer from the source or drain region, as described above.

Process 600 may include additional implementations, such as any singleimplementation or any combination of implementations described belowand/or in connection with one or more other processes describedelsewhere herein.

In a first implementation, forming the ammonium fluoride gas includesproviding a flow of ammonia gas into the processing chamber; providing aflow of nitrogen fluoride gas into the processing chamber, and causing,using a plasma source, a reaction between the ammonia gas and thenitrogen fluoride gas, the reaction between the ammonia gas and thenitrogen fluoride gas causes formation of the ammonium fluoride gas. Ina second implementation, alone or in combination with the firstimplementation, a ratio between the nitrogen fluoride gas and theammonia gas is greater than 1:5.

In a third implementation, alone or in combination with one or more ofthe first and second implementations, forming the ammonium fluoride gasincludes forming the ammonium fluoride gas to cause the chemicalreaction between the ammonium fluoride gas and the oxide layer as partof a pre-clean process. In a fourth implementation, alone or incombination with one or more of the first through third implementations,the fluorosilicic layer is a protection layer that protects the sourceor drain region from being etched.

In a fifth implementation, alone or in combination with one or more ofthe first through fourth implementations, the protection layer reducesan amount of fluorine ion etching of the source or drain region. In asixth implementation, alone or in combination with one or more of thefirst through fifth implementations, removing the fluorosilicic layerincludes heating the semiconductor device to cause the fluorosiliciclayer to decompose into a plurality of gases, and removing the pluralityof gases from the processing chamber.

In a seventh implementation, alone or in combination with one or more ofthe first through sixth implementations, heating the semiconductordevice includes heating the semiconductor device to a temperature equalto or greater than 90 degrees Celsius. In an eighth implementation,alone or in combination with one or more of the first through seventhimplementations, process 600 includes forming a metal silicide layer forthe source or drain region after removing the fluorosilicic layer. In aninth implementation, alone or in combination with one or more of thefirst through eighth implementations, process 600 includes forming acontact for the source or drain region, where the metal silicide layeris reducing contact resistance between the source or drain region andthe contact.

Although FIG. 6 shows example blocks of process 600, in someimplementations, process 600 may include additional blocks, fewerblocks, different blocks, or differently arranged blocks than thosedepicted in FIG. 6. Additionally, or alternatively, two or more of theblocks of process 600 may be performed in parallel.

FIG. 7 is a flowchart of an example process 700 associated withsemiconductor device pre-cleaning. In some implementations, one or moreprocess blocks of FIG. 7 may be performed by a semiconductor processingdevice (e.g., pre-clean tool 102, deposition tool 104, annealing tool106, plating tool 108, and/or the like). Additionally, or alternatively,one or more process blocks of FIG. 7 may be performed by one or morecomponents of a device 500, such as processor 520, memory 530, storagecomponent 540, input component 550, output component 560, communicationinterface 570, and/or the like.

As shown in FIG. 7, process 700 may include providing, as part of apre-clean process, an ammonium fluoride gas into a processing chamber(block 710). For example, the semiconductor processing device mayprovide, as part of a pre-clean process, an ammonium fluoride gas into aprocessing chamber, as described above.

As further shown in FIG. 7, process 700 may include forming, as part ofthe pre-clean process, a protection layer above a source or drain regionof a semiconductor device, where the protection layer is formed of anammonium fluoride salt from the ammonium fluoride gas, where theprotection layer protects the source or drain region from being etchedby fluorine ions during the pre-clean process, and where the protectionlayer reacts with an oxide layer on a source or drain region of asemiconductor device to remove the oxide layer from the source or drainregion (block 720). For example, the semiconductor processing device mayform, as part of the pre-clean process, a protection layer above asource or drain region of a semiconductor device, as described above. Insome implementations, the protection layer is formed of an ammoniumfluoride salt from the ammonium fluoride gas. In some implementations,the protection layer protects the source or drain region from beingetched by fluorine ions during the pre-clean process. In someimplementations, the protection layer reacts with an oxide layer on asource or drain region of a semiconductor device to remove the oxidelayer from the source or drain region.

As further shown in FIG. 7, process 700 may include removing theprotection layer after performing the pre-clean process (block 730). Forexample, the semiconductor processing device may remove the protectionlayer after performing the pre-clean process, as described above.

Process 700 may include additional implementations, such as any singleimplementation or any combination of implementations described belowand/or in connection with one or more other processes describedelsewhere herein.

In a first implementation, forming the ammonium fluoride gas includesproviding a flow of a gas mixture of an ammonia gas and a nitrogentrifluoride gas, the nitrogen trifluoride gas includes greater than 20%of the gas mixture. In a second implementation, alone or in combinationwith the first implementation, the chemical reaction between theammonium fluoride salt and the oxide layer causes formation of afluorosilicic acid salt in at least a portion of the protection layer,and removing the protection layer after performing the pre-clean processincludes removing the fluorosilicic acid salt and the ammonium fluoridesalt after performing the pre-clean process.

In a third implementation, alone or in combination with one or more ofthe first and second implementations, removing the fluorosilicic acidsalt and the ammonium fluoride salt after performing the pre-cleanprocess includes heating the semiconductor device to cause thefluorosilicic acid salt and the ammonium fluoride salt to decompose intoan ammonia gas, a hydrogen fluoride gas, and a silicon tetrafluoridegas, and removing the ammonia gas, the hydrogen fluoride gas, and thesilicon tetrafluoride gas from the processing chamber in which thesemiconductor device is located. In a fourth implementation, alone or incombination with one or more of the first through third implementations,process 700 includes forming, after removing the fluorosilicic acid saltand the ammonium fluoride salt, a contact for the source or drainregion, where the contact is being a self-aligned contact that is formedat least partially over a silicon nitride cap and a metal gate of thesemiconductor device.

Although FIG. 7 shows example blocks of process 700, in someimplementations, process 700 may include additional blocks, fewerblocks, different blocks, or differently arranged blocks than thosedepicted in FIG. 7. Additionally, or alternatively, two or more of theblocks of process 700 may be performed in parallel.

FIG. 8 is a flowchart of an example process 800 associated withsemiconductor device pre-cleaning. In some implementations, one or moreprocess blocks of FIG. 8 may be performed by a semiconductor processingdevice (e.g., pre-clean tool 102, deposition tool 104, annealing tool106, plating tool 108, and/or the like). Additionally, or alternatively,one or more process blocks of FIG. 8 may be performed by one or morecomponents of a device 500, such as processor 520, memory 530, storagecomponent 540, input component 550, output component 560, communicationinterface 570, and/or the like.

As shown in FIG. 8, process 800 may include providing an ammonia gas anda nitrogen trifluoride gas in a processing chamber to cause a reactionbetween the ammonia gas and the nitrogen trifluoride gas that forms anammonium fluoride gas in the processing chamber, where a ratio betweenthe ammonia gas and the nitrogen trifluoride gas causes an increasedamount of the ammonium fluoride gas to form (block 810). For example,the semiconductor processing device may provide an ammonia gas and anitrogen trifluoride gas in a processing chamber to cause a reactionbetween the ammonia gas and the nitrogen trifluoride gas that forms anammonium fluoride gas in the processing chamber, as described above. Insome implementations, a ratio between the ammonia gas and the nitrogentrifluoride gas causes an increased amount of the ammonium fluoride gasto form.

As further shown in FIG. 8, process 800 may include forming, from theammonium fluoride gas, a protection layer above a source or drain regionof a semiconductor device to protect the source or drain region frombeing etched by fluorine ions resulting from the reaction between theammonia gas and the nitrogen trifluoride gas (block 820). For example,the semiconductor processing device may form, from the ammonium fluoridegas, a protection layer above a source or drain region of asemiconductor device to protect the source or drain region from beingetched by fluorine ions resulting from the reaction between the ammoniagas and the nitrogen trifluoride gas, as described above.

As further shown in FIG. 8, process 800 may include cleaning, withoutuse of isotropic plasma, an oxide layer from a surface of the source ordrain region based on a reaction between the oxide layer and ammoniumfluoride in the protection layer, where the reaction between the oxidelayer and the ammonium fluoride in the protection layer causes at leasta portion of the protection layer to transition to a fluorosilicic acid(block 830). For example, the semiconductor processing device may clean,without use of isotropic plasma, an oxide layer from a surface of thesource or drain region based on a reaction between the oxide layer andammonium fluoride in the protection layer, as described above. In someimplementations, the reaction between the oxide layer and the ammoniumfluoride in the protection layer causes at least a portion of theprotection layer to transition to a fluorosilicic acid.

As further shown in FIG. 8, process 800 may include heating, aftercleaning the oxide layer from the surface of the source or drain region,the semiconductor device to remove the protection layer from the sourceor drain region (block 840). For example, the semiconductor processingdevice may heat, after cleaning the oxide layer from the surface of thesource or drain region, the semiconductor device to remove theprotection layer from the source or drain region, as described above.

Process 800 may include additional implementations, such as any singleimplementation or any combination of implementations described belowand/or in connection with one or more other processes describedelsewhere herein.

In a first implementation, the source or drain region is an epitaxialregion, and the protection layer increases an epitaxial loss window ofthe epitaxial region. In a second implementation, alone or incombination with the first implementation, heating the semiconductordevice includes heating the semiconductor device to a temperature equalto or greater than 90 degrees Celsius. In a third implementation, aloneor in combination with one or more of the first and secondimplementations, process 800 includes forming a titanium silicide layerfor the source or drain region after removing the protection layer; andforming a contact for the source or drain region, where the titaniumsilicide layer is reducing contact resistance between the source ordrain region and the contact. In a fourth implementation, alone or incombination with one or more of the first through third implementations,the protection layer is formed to a thickness in a range fromapproximately 4 nanometers to approximately 5 nanometers.

Although FIG. 8 shows example blocks of process 800, in someimplementations, process 800 may include additional blocks, fewerblocks, different blocks, or differently arranged blocks than thosedepicted in FIG. 8. Additionally, or alternatively, two or more of theblocks of process 800 may be performed in parallel.

In this way, an ammonium fluoride gas may be used to form a protectionlayer for one or more interlayer dielectric layers, one or moreinsulating caps, and/or one or more source/drain regions of asemiconductor device during a pre-clean etch process. The protectionlayer can be formed through an oversupply of nitrogen trifluoride duringthe pre-clean etch process. The oversupply of nitrogen trifluoride maybe provided by increasing the flow-in of nitrogen trifluoride relativeto a traditional amount of nitrogen trifluoride used during a pre-cleanprocess. The oversupply of nitrogen trifluoride causes an increasedformation of ammonium fluoride gas, which coats the interlayerdielectric layer(s), the insulating cap(s), and/or the source/drainregion(s) with a thick protection layer. In this way, the protectionlayer protects the interlayer dielectric layer(s), the insulatingcap(s), and/or the source/drain region(s) during the pre-clean processfrom being etching by fluorine ions formed during the pre-clean process.This may reduce the risk of an MG/MD short, may reduce SAC loss loadingfor the semiconductor device (e.g., may reduce the amount of insulatinglayer loss during the pre-clean process), may increase the epitaxialloss window for the semiconductor device (e.g., may increase thetemperature window for the pre-clean process, which may protect againsttemperature drift), and/or the like.

As described in greater detail above, some implementations describedherein provide a method. The method includes forming an ammoniumfluoride gas in a processing chamber to cause a chemical reactionbetween the ammonium fluoride gas and an oxide layer on a source ordrain region of a semiconductor device in the processing chamber. Thechemical reaction causes a fluorosilicic layer to form on the source ordrain region. The method includes removing the fluorosilicic layer fromthe source or drain region.

As described in greater detail above, some implementations describedherein provide a method. The method includes providing, as part of apre-clean process, an ammonium fluoride gas into a processing chamber.The method includes forming, as part of the pre-clean process, aprotection layer above the source or drain region. The protection layeris formed of an ammonium fluoride salt from the ammonium fluoride gas.The protection layer protects the source or drain region from beingetched by fluorine ions during the pre-clean process. The protectionlayer reacts with an oxide layer on a source or drain region of asemiconductor device to remove the oxide layer from the source or drainregion. The method includes removing the protection layer afterperforming the pre-clean process.

As described in greater detail above, some implementations describedherein provide a method. The method includes providing an ammonia gasand a nitrogen trifluoride gas in a processing chamber to cause areaction between the ammonia gas and the nitrogen trifluoride gas thatforms an ammonium fluoride gas in the processing chamber. A ratiobetween the ammonia gas and the nitrogen trifluoride gas causes anincreased amount of the ammonium fluoride gas to form. The methodincludes forming, from the ammonium fluoride gas, a protection layerabove a source or drain region of a semiconductor device to protect thesource or drain region from being etched by fluorine ions resulting fromthe reaction between the ammonia gas and the nitrogen trifluoride gas.The method includes cleaning, without use of isotropic plasma, an oxidelayer from a surface of the source or drain region based on a reactionbetween the oxide layer and ammonium fluoride in the protection layer.The reaction between the oxide layer and the ammonium fluoride in theprotection layer causes at least a portion of the protection layer totransition to a fluorosilicic acid. The method includes heating, aftercleaning the oxide layer from the surface of the source or drain region,the semiconductor device to remove the protection layer from the sourceor drain region.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

1. A method, comprising: providing a first amount of an ammonia gas anda second amount of a nitrogen fluoride gas into a processing chamber tocause an ammonium fluoride gas to form at a rate satisfying a thresholdrate; forming, based on providing the first amount of the ammonia gasand the second amount of the nitrogen fluoride gas, the ammoniumfluoride gas in the processing chamber at the rate to cause a chemicalreaction between the ammonium fluoride gas and an oxide layer on aninsulating cap, a dielectric layer, and a source or drain region of asemiconductor device in the processing chamber, wherein the chemicalreaction causes a fluorosilicic layer to form on the insulating cap, thedielectric layer, and the source or drain region, and wherein thefluorosilicic layer has a thickness greater than 14 nm over theinsulating cap and the dielectric layer; and removing the fluorosiliciclayer from the source or drain region.
 2. The method of claim 1, whereinforming the ammonium fluoride gas comprises: causing, using a plasmasource, a reaction between the ammonia gas and the nitrogen fluoridegas, wherein the reaction between the ammonia gas and the nitrogenfluoride gas causes formation of the ammonium fluoride gas.
 3. Themethod of claim 2, wherein a ratio between the nitrogen fluoride gas andthe ammonia gas is greater than 1:5.
 4. The method of claim 1, whereinforming the ammonium fluoride gas comprises: forming the ammoniumfluoride gas to cause the chemical reaction between the ammoniumfluoride gas and the oxide layer as part of a pre-clean process.
 5. Themethod of claim 1, wherein the fluorosilicic layer is a protection layerthat protects the source or drain region from being etched.
 6. Themethod of claim 5, wherein the protection layer reduces an amount offluorine ion etching of the source or drain region.
 7. The method ofclaim 1, wherein removing the fluorosilicic layer comprises: heating thesemiconductor device to cause the fluorosilicic layer to decompose intoa plurality of gases; and removing the plurality of gases from theprocessing chamber.
 8. The method of claim 7, wherein heating thesemiconductor device comprises: heating the semiconductor device to atemperature equal to or greater than 90 degrees Celsius.
 9. The methodof claim 1, further comprising: forming a metal silicide layer for thesource or drain region after removing the fluorosilicic layer.
 10. Themethod of claim 9, further comprising: forming a contact for the sourceor drain region, wherein the metal silicide layer reduces contactresistance between the source or drain region and the contact.
 11. Amethod, comprising: providing, as part of a pre-clean process, a firstamount of an ammonia gas and a second amount of a nitrogen fluoride gasinto a processing chamber to cause an ammonium fluoride gas to form at arate satisfying a threshold rate, wherein a ratio between the secondamount of the nitrogen fluoride gas and the first amount of the ammoniagas is greater than 1:5; forming, as part of the pre-clean process andbased on the ammonium fluoride gas being formed at the rate, aprotection layer above an insulating cap, a dielectric layer, and asource or drain region of a semiconductor device, wherein the protectionlayer is formed of an ammonium fluoride salt from the ammonium fluoridegas, wherein the protection layer has a thickness greater than 14 nmabove the insulating cap and the dielectric layer; wherein theprotection layer protects the source or drain region from being etchedby fluorine ions during the pre-clean process, and wherein theprotection layer reacts with an oxide layer on the source or drainregion to remove the oxide layer from the source or drain region; andremoving the protection layer after performing the pre-clean process.12. The method of claim 11, wherein providing the first amount of theammonia gas and the second amount of the nitrogen fluoride gascomprises: providing a flow of a gas mixture of the ammonia gas and anitrogen trifluoride gas, wherein the nitrogen trifluoride gas comprisesgreater than 20% of the gas mixture.
 13. The method of claim 11, whereina chemical reaction between the ammonium fluoride salt and the oxidelayer causes formation of a fluorosilicic acid salt in at least aportion of the protection layer; and wherein removing the protectionlayer after performing the pre-clean process comprises: removing thefluorosilicic acid salt and the ammonium fluoride salt after performingthe pre-clean process.
 14. The method of claim 13, wherein removing thefluorosilicic acid salt and the ammonium fluoride salt after performingthe pre-clean process comprises: heating the semiconductor device tocause the fluorosilicic acid salt and the ammonium fluoride salt todecompose into a plurality of gases; and removing the plurality of gasesfrom the processing chamber in which the semiconductor device islocated.
 15. The method of claim 14, further comprising: forming, afterremoving the fluorosilicic acid salt and the ammonium fluoride salt, acontact for the source or drain region, wherein the contact is aself-aligned contact that is formed at least partially over a siliconnitride cap and a metal gate of the semiconductor device.
 16. A method,comprising: providing a first amount of an ammonia gas and a secondamount of a nitrogen trifluoride gas in a processing chamber to cause areaction between the ammonia gas and the nitrogen trifluoride gas thatforms an ammonium fluoride gas in the processing chamber, whereinproviding the first amount of the ammonia gas and the second amount ofthe nitrogen trifluoride gas causes the ammonium fluoride gas to form ata rate satisfying a threshold rate; forming, based on the ammoniumfluoride gas being formed at the rate, a protection layer above aninsulating cap, a dielectric layer, and a source or drain region of asemiconductor device to protect the source or drain region from beingetched by fluorine ions resulting from the reaction between the ammoniagas and the nitrogen trifluoride gas, wherein the protection layer has athickness greater than 14 nm above the insulating cap and the dielectriclayer and a thickness of 4-5 nm above the source or drain region;cleaning, without use of isotropic plasma, an oxide layer from a surfaceof the source or drain region based on a reaction between the oxidelayer and ammonium fluoride in the protection layer, wherein thereaction between the oxide layer and the ammonium fluoride in theprotection layer causes at least a portion of the protection layer totransition to a fluorosilicic acid; and heating, after cleaning theoxide layer from the surface of the source or drain region, thesemiconductor device to remove the protection layer from the source ordrain region.
 17. The method of claim 16, wherein the source or drainregion is an epitaxial region; and wherein the protection layerincreases an epitaxial loss window of the epitaxial region.
 18. Themethod of claim 16, wherein heating the semiconductor device comprises:heating the semiconductor device to a temperature equal to or greaterthan 90 degrees Celsius.
 19. The method of claim 16, further comprising:forming a titanium silicide layer for the source or drain region afterremoving the protection layer; and forming a contact for the source ordrain region, wherein the titanium silicide layer reduces contactresistance between the source or drain region and the contact. 20.(canceled)
 21. The method of claim 1, further comprising: performing apre-clean process without use of isotropic plasma.